Sludge centrifuge

ABSTRACT

This invention relates to a sludge centrifuge of the type comprising a rotating drum and a conveyor worm to remove solids separated from the liquid in a drum. An improved purity of the liquid separated in the centrifuge is obtained by reducing the turbulence in the centrifuge, specifically in the separation chamber, and this is achieved by providing the centrifuge with a feed worm, by which the sludge is transported at gradually decreasing axial velocity and gradually increasing rotational velocity to the separation chamber.

United States Patent Bye-Jorgensen et al.

[ 1 Apr. 25, 1972 SLUDGE CENTRIFUGE Jorgen Steen Bye-Jorgensen,Humlebaek; Gunnar l-lartvlg Larsen, Rungsted Kyst, both of Denmark IKruger A/S, Copenhagen, Denmark Mar. 31, 1971 Inventors:

Assignee:

Filed:

Appl. No.:

Related U.S. Application Data Continuation-impart of Ser. No. 865,926,Oct. 13, 1969, abandoned.

Foreign Application Priority Data Nov. 29, 1968 Denmark ..5840

U.S. Cl ..2l0/374, 210/377 Int. Cl ..B04b 3/04 Field of Search..2l0/374, 377; 233/7 [56] References Cited UNITED STATES PATENTS834,043 10/1906 Berrigan ..23 3/7 I 1,806,241 5/1931 Dupuis ..233/73,437,209 4/1969 Evans ..2l0/374 F ORElGN PATENTS OR APPLlCATlONS297,914 l0/l928 Great Britain ..23 3/7 Primary Examiner.lim L. De CesareAttorney-Arnold Robinson [57] ABSTRACT This invention relates to asludge centrifuge of the type comprising a rotating drum and a conveyorworm to remove solids separated from the liquid in a drum. An improvedpurity of the liquid separated in the centrifuge is obtained by reducingthe turbulence in the centrifuge, specifically in the separationchamber, and this is achieved by providing the centrifuge with a feedworm, by which the sludge is transported at gradually decreasing axialvelocity and gradually increasing rotational velocity to the separationchamber.

7 Claims, 1 Drawing Figure SLUDGE CENTRIFUGE This application is acontinuation-in-part of copending application Ser. No. 865,926, filedOct. 13, 1969, and now abandoned.

The present invention relates to a sludge centrifuge comprising arotating drum containing a separating chamber for liquid and solids anda worm placed outside said chamber, for removing solids and arranged torotate at a speed differing from the rotating speed of the drum itself,and having at least one feed conduit for sludge and at least one exitopening for liquid in one end of the chamber.

Many sludge centrifuges are known in which a worm conveyor is placedinside the centrifuge drum and rotates relative to the rotating drum.This worm conveyor may be conical and placed in a conical part of thedrum so that the separated solids in more or less moist condition aredischarged at the narrow end.

In a known drum centrifuge with rotating worm, the sludge containingliquid is introduced in the drum chamber at a point between its ends,the separated solids being discharged at one end and the centrifuged(and thereby partly purified) liquid being discharged at the other end.Liquid and solids are thus moving in mutual countercurrent, and this isfound to give rise to so high a turbulence that the degree ofliquid/solid separation is usually unsatisfactory because part of thesolids return to the liquid. It is observed that such centrifuges areused, for instance, in the purification of wastewater sludge. For thispurpose, it is more important that the discharged water is virtuallyfree of sludge particles than that the solids are well drained of water,although it is desirable that the discharged solids be as well dewateredas possible. By using the drum centrifuge operating according to theabove counter-current principle for separating sludge stemming fromsewage or wastewater treatment plants, the centrifuged liquid may stillcontain about -40 percent of solids, partly in so finely dispersed formthat a removal of said solids in a subsequent precipitation orcentrifugation step will not yield a liquid of the desired degree offreedom from solids.

Realizing that turbulence causes such unsatisfactory results, it hasbeen proposed to alter the described construction of the worm in such amanner that the feed conduit for the sludge debouches in part of thedrum without any conveyor worm and provided with conical guidingsurfaces and furthermore in such a manner that an exit for purifiedliquid opens from the same drum part, this drum part being constructedas one single chamber without substantial-turbulence-creating hindrancesfor the axial and radial movements of the solids or the liquid; herebythe sludge will slide along the conical guiding surfaces to the inletend of the conveyor worm. A better separation effect is achieved by thistype of centrifuge than by the above-mentioned counter-currentcentrifuge.

It has now been found, however, that it is possible to obtain the resultthat the liquid, especially the water from wastewater sludge, isdischarged from the centrifuge in a still more purified condition thatit is possible by means of the constructions described above. This canbe obtained if, according to the invention, the inlet for the sludge issituation at the opposite end of the separation chamber through openingsin a feed worm placed coaxially with respect to the centrifuge drum andrunning in a chamber outside the separation chamber. It has been foundthat by this construction it is possible to achieve an extraordinarilyhigh purity of the liquid discharged, with as little as 0.02 percentsolids, if the feed liquid is wastewater sludge, in which case theconventional centrifuges often give contents of solids in the dischargedliquid of 0.5-1 percent. Moreover, it has been found that the centrifugeconstruction thus suggested can give this improved result with acentrifugal effect in the order of 5001,000 g, whereas conventionalcentrifuges usually operate at 2,000-3,000 g. This clearly results insignificant savings in the construction of the centrifuge.

The drum may be arranged in various ways, and the conveyor worm and thefeed worm may also be mounted in various manners. 1f the drum issubstantially conical with an outlet for solids at the narrow end, themost simple construction is obtained if, according to the invention, thefeed worm is arranged for working in contact with a surface fixedlyconnected to the conveyor worm, and for rotating at a speed differingfrom that of the conveyor wonn. Thus, the number of rotating parts iskept as low as possible. In this embodiment, the feed worm may bearranged so as to rotate at the same rotation speed as the drum itself.In this way, the mounting and driving of the various parts, especiallythe feed screw, become as simple and sturdy as possible.

In the following the centrifuge according to the invention will bedescribed more in detail with reference to the drawing, showing apreferred embodiment thereof. A conical drum 11 is placed on a suitablesupport 14 by the aid of shafts, bearings 12 and rods 13. The drum 11 ismounted on a hollow shaft 15, which, in a suitable manner, e.g., bymeans of a pulley 16, is mounted to be driven at a desired speed ofrotation n,. The power source, which may be of known or conventionaltype, is not shown. On a body 17, which is not necessarily solid, ismounted a conveyor worm 18 which includes convolutions 19. The body 17and thus the conveyor won'n 18 is fixedly connected to a shaft 20,which, for instance by the aid of a pulley 21 and a driving motor (notshown), is arranged to rotate at a speed of rotation n differing fromthe speed of n of drum 11. The relative rotation between the drum 11 andthe conveyor worm l8 scraping the drum wall should be such that thesolids deposited in the centrifuge are carried towards an exit opening22 for solids and from there are discharged through a channel 23 in thedirection shown by an arrow. The pulleys 16 and 21 might be replaced bya gear mechanism driven from one motor and giving the desired differencein revolution speed of the two shafts l5 and 20.

Sludge is conducted to the drum from a conduit 24 through a channel 25in the shaft 20. The channel 25 debouches in openings 26 into a chamber51 in which is placed a feed worm 53. In the embodiment shown, theopenings 26 lead through a fixed coupling 27, the shaft 20 at this placebeing divided into two parts mutually fixedly connected by the aid ofthe coupling 27, but the shaft 20 may also be continuous. Moreover,there is in the shown embodiment a channel 28 at the left end of theshaft 20 (the orientation of the figure); it is in connection with aconduit 29 and debouches in the drum space with openings 30. Throughconduit 29, channel 28 and openings 30 there may, if desired, be fedchemicals for treatment of the feed sludge in order to facilitate theseparation. The inlets may also be interchanged, so thatsludge-containing liquid is fed through conduit 29 and a solution or asuspension and chemicals through the conduit 24. Chemicals may also beadded in any other known manner.

The feed wonn 53 is mounted on a body 34 which is not necessary solidand which is fixedly connected to the shaft 15, to which shaft the drum11 too is fixedly connected. During the operation of the centrifuge, thebody 34 consequently rotates at the speed n, of the drum ll. Feed worm53, being mounted on the body 34, also rotates at the speed n,. Whensludge is fed through the conduit 24, the channel 25 and the openings26, it can only continue through the chamber 51 by passing the feed worm53. As shown in the drawing, the feed worm 53 has an outer diameterwhich increases as the feed wonn 53 extends along the length of body 34from feed chamber 51 to separation chamber 31. The sludge which istransported by feed worm 53 in an axial direction from feed chamber 51to separation chamber 31 undergoes a gradual decrease in axial velocitydue to increased cross-section while simultaneously being subjected toincreasing tangential velocity as a consequency of the gradually variedvelocities. Turbulence within wonn 53 is greatly reduced, and thereforethe sludge enters the separation chamber 31 in a state of insignificantturbulence. The lack of turbulence in the separation chamber 31 ismaintained due to the absence of any moving members in that chamber,thereby enabling the settling out even of fine solid particlesv Feedworm 53 scrapes against the inside 33 of the body'17, that is inpractice against the inside of the conveyor worm 18, which rotates atthe speed n (slightly different from speed n,) and has transportdirection from left to right (in the orientation of the drawing).Through openings 55 the feed worm delivers the sludge conveyed by itinto the separation chamber 31 at the right end of the drum (in theorientation of the drawing). In the embodiment shown, the chamber 31 isin one end limited by the feed work 53 and the body 34, at the other endby the end wall of the drum. in this end wall there are openings 36 fordischarging separated liquid. From the chamber 31 there is also entranceto the intake end 39 of the conveyor worm 18, through which intake endthe separated solids pass. Thus, the liquid leaves the drum throughopenings 36, the size and exact placing of which may be adjustable,e.g., by aid of an opening having variable size. The place of theopenings 36 determines the liquid surface in the centrifuge, suggestedby the two broken lines 37.

The presence of the feed worm 53 causes a quiet, turbulence-free flow tothe separation chamber 31 and causes the liquid to depart from thatchamber through openings 36 in an extremely pure condition.

The entire machine may be encased in a housing and the liquid from theopenings 36 may depart through a channel 38 in the direction shown by anarrow.

If desired, the embodiment shown may be altered so that the body 34 andthereby the feed worm 53 rotates at a rotation speed differing from boththat of drum l1 and that of the conveyor worm 18, but that gives asomewhat more complicated suspension and requires a third shaft coaxialto the other two shafts 15 and 20.

The advantages of the present invention, as well as certain changes andmodifications of the disclosed embodiment thereof, will be readilyapparent to those skilled in the art. It is the applicants intention tocover all those changes and modifications which could be made to theembodiment of the invention herein chosen for the purpose of thedisclosure without departing from the spirit and scope of the invention.

What is claimed is:

l. A centrifuge for separating water from wastewater sludge andcomprising:

l. rotatably mounted drum means with a horizontal shaft and having animperforate side wall and an end wall;

2. conveyor worm means rotatably and c'oaxially mounted within said drummeans;

3. feed worm means rotatably and coaxially mounted within said conveyorworm means;

4. a feed chamber within said conveyor worm means;

5. a separation chamber formed between said end wall of said drum meansand said conveyor worm means and said feed worm means, said separationchamber being free of turbulence-creating obstructions and having atleast one outlet formed in said end wall for the removal of liquidtherefrom, said conveyor wonn means being operative to remove dewateredsludge from said separation chamber by rotating relative to said drummeans;

6. conduit means operative to introduce said sludge into said feedchamber, from which said mixture is transported into said separationchamber at decreasing axial velocity and increasing tangential velocityby said feed worm means; and

7. support means for mounting said drum means, conveyor means, and feedworm means,

2. The centrifuge according to claim 1 wherein said drum means isgenerally conical in shape, and said horizontal shaft is hollow.

3. The centrifuge according to claim 2 wherein said conveyor worm meansis generally cortical in shape, and further includes a second hollowshaft to enable said conveyor worm means to be rotatably driven.

4. The centrifuge according to claim 3 wherein said second hollow shaftis coaxially disposed within said first hollow shaft for at least aportion of its length.

5. The centrifuge according to claim 3 wherein said conveyor worm meanshas a hollow larger end. said feed worm means being mounted within saidhollow larger end and being mounted on said first hollow shaft.

6. The centrifuge according to claim 3 wherein said second hollow shaftincludes said conduit means.

7. The centrifuge according to claim 1 wherein said feed worm meanscomprises a feed worm increasing in diameter as it extends from saidfeed chamber to said separation chamber.

1. A centrifuge for separating water from wastewater sludge andcomprising:
 1. rotatably mountEd drum means with a horizontal shaft andhaving an imperforate side wall and an end wall;
 2. conveyor worm meansrotatably and coaxially mounted within said drum means;
 3. feed wormmeans rotatably and coaxially mounted within said conveyor worm means;4. a feed chamber within said conveyor worm means;
 5. a separationchamber formed between said end wall of said drum means and saidconveyor worm means and said feed worm means, said separation chamberbeing free of turbulencecreating obstructions and having at least oneoutlet formed in said end wall for the removal of liquid therefrom, saidconveyor worm means being operative to remove dewatered sludge from saidseparation chamber by rotating relative to said drum means;
 6. conduitmeans operative to introduce said sludge into said feed chamber, fromwhich said mixture is transported into said separation chamber atdecreasing axial velocity and increasing tangential velocity by saidfeed worm means; and
 7. support means for mounting said drum means,conveyor means, and feed worm means.
 2. conveyor worm means rotatablyand coaxially mounted within said drum means;
 2. The centrifugeaccording to claim 1 wherein said drum means is generally conical inshape, and said horizontal shaft is hollow.
 3. The centrifuge accordingto claim 2 wherein said conveyor worm means is generally conical inshape, and further includes a second hollow shaft to enable saidconveyor worm means to be rotatably driven.
 3. feed worm means rotatablyand coaxially mounted within said conveyor worm means;
 4. a feed chamberwithin said conveyor worm means;
 4. The centrifuge according to claim 3wherein said second hollow shaft is coaxially disposed within said firsthollow shaft for at least a portion of its length.
 5. The centrifugeaccording to claim 3 wherein said conveyor worm means has a hollowlarger end, said feed worm means being mounted within said hollow largerend and being mounted on said first hollow shaft.
 5. a separationchamber formed between said end wall of said drum means and saidconveyor worm means and said feed worm means, said separation chamberbeing free of turbulence-creating obstructions and having at least oneoutlet formed in said end wall for the removal of liquid therefrom, saidconveyor worm means being operative to remove dewatered sludge from saidseparation chamber by rotating relative to said drum means;
 6. conduitmeans operative to introduce said sludge into said feed chamber, fromwhich said mixture is transported into said separation chamber atdecreasing axial velocity and increasing tangential velocity by saidfeed worm means; and
 6. The centrifuge according to claim 3 wherein saidsecond hollow shaft includes said conduit means.
 7. The centrifugeaccording to claim 1 wherein said feed worm means comprises a feed wormincreasing in diameter as it extends from said feed chamber to saidseparation chamber.
 7. support means for mounting said drum means,conveyor means, and feed worm means.